Transparent sheet material



Patented @ct. 9, 1934 ABA TRANSPARENT SHEET MATERIAL tion of Illinois NoDrawing. Application July 8, 1927, Serial No. 204,422

8 Claims.

' This invention relates to transparent sheet material and moreparticularly to a coated gelatine composition sheet adapted for wrappingpurposes.

Heretofore, gelatine has been considered unsuitable for the manufactureof waterproof wrapping material, because, although the gelatine may berendered insoluble by the use of tanning agents, a tanned gelatine sheetwill still permit the passage of moisture through it. Cellophane(cellulose xanthate) is also objectionable in this respect, since ittakes water only about 10 seconds to pass through a sheet of cellophane.001 inch thick. Sheets of cellulose nitrate or acetate are in generalwaterproof but rather expensive of manufacture.

It is therefore an object of this invention to provide an inexpensivetransparent, flexible wrapping material made of gelatine or gelatinecomposition as a base and having a waterproof coating of a celluloseester or mixture of esters.

Other and further important objects of this invention will becomeapparent from the disclosures in the following description and appendedclaims.

The present invention consists in coating a straight gelatine film or afilm made from gelatine and sulphonated cfiastor oil, as disclosed in myco-pending applic tion, Serial No. 10,962, filed February 21, 1925, witha cellulose ester, such as cellulose nitrate or acetate, or a mixture ofthe two. The gelatine or gelatine-sulphonated oil composition may beformed as a film upon any suitable surface from which it may be readilystripped when dry. I prefer to use the coated fabric surface or beltdisclosed in my co-pending application, Serial No. 11,335, filedFebruary 24, 1925, wherein the surface is formed of baked drying oils.If a gelatine composition base is to be used, I prefer a compositionsuch as disclosed in my co-pending application, Serial No. 10,962,comprising approximately 60 to 85% glue and to sulphonated castor oil.Preferably no tanning agent is used.

The gelatine, or gelatine-composition film is then coated with cellulosenitrate, or acetate, or a mixture of the two, either on one or bothsides of the film. Cellulose acetate being noninfiammable, it ispossible to prepare a mixture of the two esters wherein the celluloseacetate contact is sufiiciently high to render the mixture alsonon-inflammable.

The coating is preferably effected by means of p a doctor. A surplus ofthe coating material dissolved in a volatile solvent is deposited on thetraveling film ahead of the doctor and the excess scraped off by thedoctor, thus leaving a uniform thin coating on the film. The evaporationof the solvent is preferably effected while the film is passing undertension over a curved surface, so as to prevent the edges of the filmfrom curling. Obviously, the process may be made continuous if desired.

Where the sheet material is to be used for making bags or for somewrapping purposes, it is preferable to coat the gelatine base film onbut one side. The sheet material is then self sealing, since theapplication of moisture to the uncoated surfaces render them adhesive.For other purposes the sheet may be coated on both sides.

While I do not wish to limit the composition of the sheet material toany specific proportions, the following will serve to illustrate mypreferred composition:

Per cent Ethyl acetate 14 Butyl acetate 27 Toluene--- 14 Cellulosenitrate and acetate (1 to 2) 23 Alcohol (denatured #1) 6 Benzene 3Dammar gum 8 Tri-cresyl-phosphate 5- In place of tri-cresyl-phosphate,any suitable plasticizer may be used. Other satisfactory solvents forthe cellulose esters will also occur to those familiar with the art.

I am aware that numerous details of the process may be varied through awide range without departing from the principles of this invention andI, therefore, do not purpose limiting the patent granted hereon,otherwise than necessitated by the prior art.

" I claim as my, invention:

1. A transparent self-sustaining sheet compris ing a gelatinous basehaving a water proof coating of cellulose nitrate, cellulose acetate andtricresyl phosphate.

2. A transparent self-sustaining sheet comprising a gelatinous basehaving a water proof coating of cellulose nitrate, cellulose acetate,tricresyl phosphateand dammar gum.

3. A transparent self-sustaining sheet comprising a base formed ofgelatine and sulphonated castor oil and having'a water proof coatingcomprising one part cellulose nitrate to two parts cellulose acetatewith small amounts of tri-cresyl phosphate and dammar gum.

4. An integral, transparent wrapping sheet comprising a thin film ofgelatine as a base, a coating of cellulose nitrate applied to each faceof said film and having incorporated therein a plasticizer, thecellulose nitrate coating being integrally united with the gelatine oneach side thereof and the thickness of saidi'film ing respectively beingsuch that. said-resultant wrapping sheet will he flexible, transparentand waterproof and adapted to conform readily to the shape of packagesand the like without cracking or separating.

5. An integral, transparent wrapping sheet comprising a thin film ofgelatine as a base, a coating of cellulose nitrate applied toeach faceof said film and having incorporated therein tricresyl phosphate. p

6. An integral transparent wrapping. sheet of the character describedconsisting of a thin film of a protein substance as abase, a coating ofcellulose nitrate applied to each face of said film and havingincorporated therein anon-hygroscopic bonding agent (other than castoroil) in such a quantity as to cause the cellulose nitrate coating tobecome integrally unitedwith the protein film on each side thereof, thethickness of the said film and coating respectively being such as thatsaid resultant wrapping sheet will be tough, pliable, transparent,moisture, grease and water proof and adapted to readily conform to andcoata coating of a cellulose the shape of packages and the likewithoutcracking or separating.

7. An integral transparent wrapping sheet of the character describedconsisting of a thin film of a protein substance as a base, a coating ofcellulose nitrate applied to each face of said film and havingincorporated therein a non-hygroscopic bonding agent (other than castoroil) in such a quantity up to 30% by weight of the dried coating ofcellulose nitrate as to cause the cellulose nitrate coating to becomeintegrally united with the protein film on each side thereof, thethickness of the said film and coating respectively being such as thatsaid resultant wrapping sheet will be tough, pliable, transparent,moisture, grease and water proof and adapted to readily conform to theshape of packages and the like without cracking or separating.

8. An integral transparent wrapping sheet comprising a thin film ofprotein material as a base, derivative selected from the groupconsisting of cellulose nitrate and a mixture of cellulose nitrate andcellulose acetate applied to said film and having incorporated therein aplasticizer, the cellulose derivative coatq ing being integrally unitedwith the base, the thickness of said base and coating being such thatthe said resulting Wrapping sheet will be flexible, transparent, andwaterproof and adapted to conform readily to the shape of packages andthe like without cracking or separating.

EDOUARD M. W12.

